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This award-winning blog supplements the articles in Hospital Infection Control & Prevention.

Flu vaccine 62% effective, but one B strain of virus not covered

The effectiveness of the current influenza vaccine is 62% and covers about 90% of the circulating virus, the Centers for Disease Control and Prevention reports. Unfortunately, the very groups at greatest risk of flu infection also are less likely to mount an immune response following vaccination.

“That would include frail, elderly, people who may have had cancer, chemotherapy, people who may have immune systems that are weakened or be on medications that would weaken their immune system, including people who are on long-term oral steroid treatments for conditions that require that,” Tom Frieden, MD, CDC director said at a recent press conference. “It's kind of the opposite of what we'd wish. The people who are most susceptible to severe influenza are also less likely to get the benefit that others get from the vaccine.”

To analysis the efficacy of the vaccine, the CDC looked at 1,155 children and adults in its flu effectiveness network program. “We found the overall vaccine effectiveness to be 62% -- that means that if you got vaccinated you’re about 60% less likely to get the flu that requires you to go to your doctor. “

That puts the vaccine efficacy in line with most seasons, which has been generally estimated year-in year-out at about 59%.

“We have known for a long time is that the flu vaccine is far from perfect,” Frieden said. “But it's still by far the best tool we have to prevent the flu.”

The vaccine covers for the two most common circulating A strains including Influenza A (H3N2), and one B strain of influenza. However, another circulating B strain is not in the vaccine, reflecting the limitations of the current manufacturing technology. “Within a year or two, we expect manufacturers to have on the market vaccines that have space for four different vaccine [strains] including two influenza B’s,” he said.